When a bar, beam etc., is deflected by a cross-strain, the ode of the beam, etc., which is bounded by the concave sur. face, is compressed, and the opposite side is extended.

In stones and cast metals, the resistance to compression is greater than the resistance to extension.

In woods, the resistance to extension is greater than the resistance to compression.

The general law regarding deflection is, that it increases, caeteris paribus, directly as the cube of the length of the beam, bar, etc., and inversely as the breadth and cube of the depth.

The resistance of flexure, of a body at its cross-section is very nearly 9-10 of its tensile resistance.

The stiffest bar or beam that can be cut out of a cylinder is that of which the depth is to the breadth as the square root of 3 to 1; the strongest, as the square root of 2 to 1: and the most resilient, that which has the breadth and depth equal.